Nissan XTerra Forum banner

HDPE skid plate

30K views 36 replies 25 participants last post by  Xterra Mike 
#1 ·
For the better part of the past year I've been contemplating making a set of HDPE skids. The OEM skids had worked well but the gas tank skid had a crease that was pressing against the gas tank. That and the fact that the front diff and tranny were unprotected. Last fall's run down Jenny Creek convinced me that better armor was necessary. Problem is, I already have a bunch of added weight on my truck, and I tow a good size travel trailer. I therefore wasn't keen on the extra 140 pounds for the Shrockworks stuff. There is a commercial HDPE skid for the FJ that seems to be working well, so I figured, why not try it.

The next issue was cost. Shipping anything over a 2'x4' sheet would get expensive quick. I came up with a plan to use 2 or 3 sheets this size, but then I'd have to worry about catching the edges where sheets meet on a rock. I made some calls to local plasitcs places and found one that would sell me a 4'x10'x1/2" sheet of HDPE for $185 and there was no freight charge. With this size sheet I could cover the oil pan & front diff, tranny, transfer case, and gas tank with one sheet. I'd also be able to go from frame rail to frame rail.

Here is the sheet on top of the truck.



Based on the density of HDPE, I estimate that the whole sheet weighs 100 lbs.

The next concern was to minimize the span that the HDPE would cross without support. I also needed a way of supporting the skid around the gas tank (especially the aft end). I picked up a couple of 3/16"x-1/2"x4' bars of steel along with a 1/8"x1-1/2"x4' steel angle at Home Depot. With these I fabbed up 3 support pieces.



The angle piece runs frame rail to frame rail behind the TC but in front of the exhaust cross-over.



One piece of flat stock runs from the driver side frame rail to that support that straddles the rear drive shaft.




The last piece of flat stock supports the aft end of the gas tank. It uses the OEM threaded hole near the drive shaft at one and an one in the wheel well at the other.







Since I haven't welded in 25 years, and I wanted these done for Moab, I decided to go with a bolt on solution. Having worked in the aircraft industry, I was familiar with rivnuts and decided these would be a slick solution. I stuck with the 8mm x1.25 thread of the OEM bolts.






With the supports fabbed and the fixation worked out, it was time to start cutting some plastic. First I made a carboard template with all the OEM holes laid out on it. One of the nice things about HDPE is that you can use standard woodworking tools. I used a circular saw for the straight cuts, a jig saw for the inside corners and curves, and a drill for the holes (duh). I rough cut the sheet and then installed it so that I could drill holes through the sheet and frame rails where I wanted them. I then took the sheet off and finished shaping and drilling it.


In order to not have to do a bunch of bending to clear the front diff, TC, gas tank, etc., I chose to make some spacers between the sheet and the relevant frame pieces.



So the skid is now mounted up, minus a few bolts. A quick run to the hardware store will take care of that. Here is a shot of it in the meantime.



My remaining concerns are with the front edge and with heat.

The front edge of the skid is just begging to get caught on a rock. I tried heating it up so that I could bend it to a better profile, but that wasn't enough. I'm going to make a thin metal plate to cover the bottom of the Shrockworks radiatior skid and the front of the HDPE skid.

My concern with heat is that the tranny is now pretty much full enclosed with the CATs. I’ll monitor the tranny temp on my way to Moab and will drill some cooling holes if necessary. I think that there will be enough air flowing through so this won’t be an issue, but I definitely want to watch it. I'll also have to keep an eye on it next time I'm towing.
 
See less See more
11
#7 ·
How is the heat situation going?

Chuck
 
#8 ·
How is the heat situation going?

Chuck
The heat trapped underneath didn't seem to affect the tranny temps (though I've since added and aux cooler). There has been enough heat though to cause the skid to deform. The problem is rear of the CATS, and in particular around the exhaust pipe that runs from the driver side CAT to the Y pipe. I've cut additional cooling holes, but that hasn't been enough. I'm trying to decide between cutting more, or wrapping the exhaust between the CATS and the muffler. The second solution would help keep the TC cool in addition to helping the skid, but I've heard mixed opinions on the effects of exhaust wrap on the pipes.
 
#9 ·
Does this heat situation occur with the shrock skids too?

Chuck
 
#10 ·
Does this heat situation occur with the shrock skids too?

Chuck
I never had the full set of Shrock skids but haven't heard anyone complain of heat buildup. One difference could be that the metal will conduct some of the heat away whereas the HDPE will act as an insulator and trap it between the skid and the floor (except for airflow through the space).
 
#12 ·
have you yet tested the skid plate and its protection abiality? wonder how UHMW would stand up as well.
I've taken some mild/moderate hits, but nothing big. Other than some scratches the skids are fine. They do not like the exhaust heat though. The plastic melted pretty good around the cross-over pipe coming from the driver's side CATS to the Y pipe and muffler.
 
#13 ·
so basically these cost less than shrock skids, are a lot lighter, and they possibly hold up fairly well?
 
#15 ·
hmm what about a thin sheet of aluminum on top of it to help disburse heat? not sure if that would help. just a thought.
 
#17 ·
HDPE is some pretty strong stuff. The only downside to it is heat does affect it (obviously, it's a plastic) and unless you get it with added UV protection sunlight makes it brittle pretty quick.

UHMWPE (Ultra high molecular weight polyethylene) is really strong, is used for all sorts of stuff (artificial joints, bullet proof vests, etc) and would seem like it would really hold up to off-road abuse if it wasn't more expensive than HDPE. MDPE would be a good option too as it has great shock and drop resistance and not at "notch sensitive" as HDPE.

The downside is, HDPE is hard to repair. Canoes and Kayaks tend to use PEX (fits between MDPE and HDPE), and a lot of adhesives don't bond to the higher density PE's. 3M makes some but it's crazy expensive (dp-8005 if I remember correctly). Trust me, repairing canoes and kayaks suck (I do it on the side). If the plastic does melt the whole way and you end up with a hole, the only real way to fix it, being HDPE, is to actually melt more HDPE back into the sheet, heating and working it until the new piece and old piece are throughly mixed together.

One thing you could try for the heat, since it's basically radiated heat, it spraying the back side of the PE with a chrome or aluminum finished paint. Even a layer of smooth tinfoil could potentially help, though it would rip pretty quick. Since HDPE has an almost oily quality to it, you may have to scuff it fairly well before painting to get the paint to stick, and do quite a few layers so it's smooth. It may not help much, but it may be worth a try.
 
#18 ·
.... UHMWPE (Ultra high molecular weight polyethylene) is really strong, is used for all sorts of stuff (artificial joints, bullet proof vests, etc) and would seem like it would really hold up to off-road abuse if it wasn't more expensive than HDPE. MDPE would be a good option too as it has great shock and drop resistance and not at "notch sensitive" as HDPE.....
http://www.grainger.com/Grainger/plastic-sheets-film-and-flat-stock/plastics/raw-materials/ecatalog/N-c1pZ1z12utq?op=search
 
#21 ·
Not sure if this was mentioned or not, but I'm sure everyone came up with the idea of using this stuff as skid plates from seeing it on rock crawler buggies. But what I'm not sure about is if anyone knows that the HDPE is only a top sheet "skid" They use primary skids against the body/belly pan, and then put this stuff on top of it to help them "slide" over rocks. They don't use it alone as it dosen't really provide a lot of protection, it aids in going over rocks and its easily replaceable.

So I wouldn't see HDPE as an alternative to metal skids, see it as an addition to skids
 
#22 ·
I have just the 1/4 inch HDPE Skids under my transfer case and engine. I needed more protection rather than havin nothing at all. I don't do anymore agressive offroad drivin cause i have the skids but its nice to know at least there is something under there. They have worked fine for me.

 
#23 ·
I have just the 1/4 inch HDPE Skids under my transfer case and engine. I needed more protection rather than havin nothing at all. I don't do anymore agressive offroad drivin cause i have the skids but its nice to know at least there is something under there. They have worked fine for me.

LOL @ the Front arrow

Kneebuster, rep points for the writeup
 
#24 · (Edited)
I really like the write up. It looks great too as one solid piece from front to back. I think I'd like to try the same thing in black on my 1st Gen.
I found this on a WRX site. Do you think this would help to distribute the heat well enough to prevent melting? Maybe something larger would help.



Can you post a pic of the skid as it rides today? Is it noticeably warped from the heat of the exhaust?
Does your engine run any warmer without the ability to drag cooler air across the bottom of the engine?
 
#25 ·
I really like the write up. It looks great too as one solid piece from front to back. I think I'd like to try the same thing in black on my 1st Gen.
I found this on a WRX site. Do you think this would help to distribute the heat well enough to prevent melting? Maybe something larger would help.

Can you post a pic of the skid as it rides today? Is it noticeably warped from the heat of the exhaust?
Does your engine run any warmer without the ability to drag cooler air across the bottom of the engine?

Sorry for not responding sooner, I haven't logged on in several months.

A thin metal sheet might help with the heat. As it was, they skids really didn't like the heat of the exhaust.


So I trimmed it further forward of the crossover and made a new rear piece. Obviously I no longer have a single skid front to back.

If I were to do it again I'd either wrap the exhaust or use some sort of thin metal plate.

There has been no increased engine or tranny temps as a result of the skids.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top